| Ammannia arenaria is one of the most harmful weeds in paddy rice fields in China. The indoor and field experiments were conducted to determine the resistant levels of A. arenaria to bensulfuron-methyl, and to compare the biological characteristics of susceptible biotype and resistant biotype of A. arenaria, also the competition of A. arenaria with paddy rice and resulting effect on rice yield were conducted. It is very helpful for evaluation of the harmful level and resistance risk of fields, arenaria and its management.(1) The indoor and field experiments were conducted to determine the resistant levels of A. arenaria to bensulfuron-methyl. The results by method of emergence test in agar showed that the A arenaria biotypes HZ018-04, HZ018-06and HZ001from Hangzhou are susceptible to bensulfuron-methyl. The biotypes NB0143-01, NB0145-02, NB0143-05from Ningbo are resistant to the herbicide with the resistance index (R1)124.4,55.0and45.042.7, respectively. Biotype SX022(from Shaoxing), JX007-01and JX013-01(from Jiaxing) are also resistant to the herbicide with the RJ55.1,42.7and32.4, respectively. The results of potted experiments showed that the RI of the biotype NB0143-05is43.3. Field experiments showed that under normal dosages49.4gai/ha, bensulfuron-methy had little effect on growth of A. arenaria. These results indicated that the A. arenaria from regions of Ningbo, Shaoxing and Jiaxing in Zhejiang province were highly resistant to bensulfuron-methyl. This was the first report of A. arenaria resistance level to bensulfuron-methyl.(2) Pretreated with dark and poikilothermic treatment in30℃(12h)/15℃(12h) for15days, the germination rates of the seeds of A, arenaria were significant increased. The results showed that biotypes JX013-01, NB0143-06, NB046-01, NB046-06were at least6times more than, that of CK, this was very helpful for exact identification of the resistant level of A. arenaria.(3) There were differences between resistance biotype (NB143-05, RB) and susceptible biotype (HZ001, SB) of A arenaria to bensulfuron-methyl in field experiments. The emergence dynamic of RB seeds were similar to SB with two emergence pinks of4-6and12days after seeding(DAS), and the emergence was as long as40days. The RB, with lower plant height, fewer branches, less and smaller leaves and less capsules, but little difference was found concerning the seed number per capsule. The above ground part, underground part and whole plant dry weight of SB were68.3g,7.0g and75.3g, respectively. However those of RB plant were54.4%,55.1%and54.5%less than that of SB, respectively. But early florescence and florescence time of RB were16days earlier than that of susceptible biotype, which might contributes to its strong adaptive ability in the paddy rice field.(4) The competition experiments of paddy rice with SB (HZ001) and RB (NB143-05) of A. arenaria biotypes were conducted in basins in field. Compared to the A. arenaria biotypes, the paddy rice was dominated before45DAS, significantly higher than both A. arenaria biotypes, then the height becoming similar at50DAS, but rice was significant lower than the A. arenaria biotypes after55DAS. The effect of RB on the tillerings of paddy rice were more serious at the beginning than that of SB under both low density (58plants/m2) and high density (288plants/m2), for instance, the number of tillerings of paddy rice under competition with RB was40.3%lower than that of under SB (0.7tillerings per plant) at35DAS in low density. But at later stage, the effect of RB on tillerings was similar or lower than that of SB. For example, at80DAS, the number of tillerings of the control was1.0per plant, under competition with SB and RB that were decreased by71.2%and59.5%, respectively. When paddy rice came into maturity at141DAS, the number of rice spikes of the CK was18.7per0.063m2. Under low density competition, the effects of two biotypes on rice spikes were not significantly different, while under high density, the number of spikes were significant decreased by90.2%for SB and62.5%for RB, respectively. The result indicated that at early stage the effect of RB on tillerings of paddy rice was more serious than SB, but the effect on yield was smaller than SB, the harmful level of RB to paddy rice was reduced to some extent.(5) With the increasing of A. arenaria density in field, the branches and dry weight of A. arenaria decreased. When the paddy rice came into maturity (136DAS), the height of A. arenaria in different densities treatment was almost same. But compared to5plants/m2, the number of branches was decreased by11.3%at50plants/m2. When the density increased to30plants/m2, the dry weight per plant was significant decreased, it was decreased by20.4%comparing to that of5plants/m2treatment.With the increasing of A. arenaria density, the number of tillerings, the spikes and yield of the paddy rice were significant decreased. When the density increased to5plants/m2in field, the number of tillerings, the spikes and yield of the paddy rice were18.7%and22.2%significant less than those of the control, respectively. At the densities of10,20,30,40,50plants of A. arenaria per square meter, the yield of paddy rice were decreased by30.8%,41.2%,53.3%,61.2%and70.3%, respectively. The result indicated that when the density of A. arenaria was as less as5plants/m2, the number of spikes and yield of paddy rice were greatly decreased; with the increasing of A. arenaria density, the harm was increased. |
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